A 6-aminopenicillanic acide nucleus composed of a thiazoldiline ring fused to a beta-lactam ring

Why is Ring B important?

Ring B is:
1. the active center of the
antibiotic,
2. the site of action of bacterial enzymes (βlactamases and penicillinases)
3. the site of formation of the "major" antigenic determinants of the penicillins

Alterations in the R group change what properties of the penicillin molecule?

1. Full spectrum (except when resistant)
2. (Peni/Cephalo)Inhibition of the synthesis of crosslinks between the repeating disaccharide subunits of the bacterial cell wall.
These antibiotics are structural analogues of the D-ala-D-ala substrate for the transpeptidase and form a covalent complex which is inactive.
These ABs bind to PBPs that catalyze or participate ion a variety of rxs necessary for the synthesis &
maintenence of the cell wall.
β Lactam Abs also activate/disinhibit autolytic enzymes which normally fxn to break down the cell wall during cell growth and division.

Skin testing is often used. Challenge with the major determinant (pre-pen) will predict about 95% of IgE-mediated hypersensitivity. soooo, even a neg test doesn't guarantee the absence of an anaphyllactic response
RAST is used to detect penicilloyl-specific IgE ab wo skin testing, results comparable to skin testing.

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